Steam Explosion Pretreatment of Lignocellulosic Biomass: A Mini-Review of Theorical and Experimental Approaches

Steam Explosion (SE) is one of the most efficient and environmentally friendly processes for the pretreatment of lignocellulosic biomass. It is an important tool for the development of the biorefinery concept to mitigate the recalcitrance of biomass. However, the two distinct steps of SE, steam cracking and explosive decompression, leading to the breakdown of the lignocellulosic matrix have generally been studied in empiric ways and clarification are needed. This mini-review provides new insights and recommendations regarding the properties of subcritical water, process modeling and the importance of the depressurization rate.

A novel surfactant-assisted dilute phosphoric acid plus steam explosion pretreatment of poplar wood for fermentable sugar production

Pretreatment is an indispensable process in lignocellulosic bioethanol production. In this work, a surfactant agent JFC was introduced into the dilute phosphoric acid plus steam explosion pretreatment scheme for fermentable sugar production using poplar as substrate. Four crucial factors (phosphoric acid concentration, surfactant concentration, pressure, and residence time) affecting the pretreatment efficiency were optimized using the single factor tests. The optimal parameters obtained were as follows: 1:2.5 solid/liquid rate, 2 h pre-soaking time, 1.5 %(v/v) JFC-M + 2.0 wt% phosphoric acid, 2.0 MPa pressure, and 120 s residence time, resulting in a maximum cellulose recovery rate of 86.33 % and enzymatic saccharification rate of 84.62 %, which was 38.97 % higher than that of control. The morphological and structural characteristics of samples before and after pretreatment, were characterized by the scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) method. The addition of JFC-M was of a notable influence in overcoming biomass recalcitrance and boosting cellulose digestion, showing great application potentials in biomass conversion process.

Effects of steam explosion pretreatment on the extraction of xylooligosaccharide from rice husk

Rice husk, which contains hemicellulose, can be used as a renewable resource to produce xylooligosaccharide (XOS). However, it is difficult to destroy the lignin structure of rice husk. Steam explosion (SE) is an effective method in destroying the lignin structure to enhance the release of hemicellulose and cellulose. In this study, SE pretreatment was used at different high pressures. The results showed that the lignin structure of rice husk could be collapsed by SE pretreatment, and the chemical structures of rice husk were evaluated by Fourier transform infrared spectroscopy (FTIR). The SE pretreatment resulted in the significant increase of XOS content and antioxidant activities. In summary, SE pretreatment under 2.5 MPa was chosen as a good option for the production of XOS from rice husk.

Effect of Semi-Continuous Anaerobic Digestion on the Substrate Solubilisation of Lignin-Rich Steam-Exploded Ludwigia grandiflora

In this study, semi-continuous anaerobic digestion of lignin-rich steam-exploded Ludwigia grandiflora (Lignin = 25.22% ± 4.6% total solids) was performed to understand better the effect of steam explosion on the substrate solubilisation and inhibitors formation during the process. Steam explosion pretreatment was performed at 180 °C for 30 min at a severity factor of 3.8 to enhance the biogas yield of the lignocellulosic biomass. The semi-continuous anaerobic digestion was performed in a continuously stirred tank reactor for 98 days at an initial hydraulic retention time of 30 days and an organic loading rate of 0.9 g-VS L−1day−1. The performed steam explosion pretreatment caused biomass solubilisation, resulting in enhanced biogas production during the process. During the anaerobic digestion process, the average biogas yield was 265 mL g-VS−1, and the pH throughout the operation was in the optimum range of 6.5–8.2. Due to fluctuations in the biogas yield, the hydraulic retention time and organic loading rate were changed on day 42 (50 days and 0.5 g-VS L−1day−1) and on day 49 (40 days and 0.7 g-VS L−1day−1), and 1 M of NaOH was added to the liquid fraction of the steam-exploded L. grandiflora during the latter part of the operation to maintain the stability in the reactor. Therefore, the steam explosion pretreatment helped in the degradation of L. grandiflora by breaking the lignocellulose structure. In addition, changes in the operating conditions of the anaerobic digestion led to an increase in the biogas production towards the end of the process, leading to the stability in the CSTR.